Acoustic transformer



June 5, 1928.-

. 1,672,472 P. A. ROBBINS I ACOUSTI C TRANSFORMER Filed April' 1, 1927 INVENIEURQ Patented June 5, 1928.

PATENT orrlcs.

PERCY A. ROBBINS, OF HIGHLAND PARK, ILLINOIS.

ACOUSTIC TRANSFORMER.

Application filed s in 1, 1927. Serial No. 180,296.

This invention relates to methods of and apparatus for-converting the movements of a iaphragm into sound waves or vice versa,

. such as shown and described in my copending application'No. 180,295 datedApr. 1st,

1927. In the transformer described in thatapplication I caused the vibrations of a diaphragm to:be imparted to or received from a stream of a gaseous medium contacting with the diaphragm, which medium is preferably, initially, ina state of compression and is allowed to expand after medium mingles with ,the atmosphere and i is lost. I was thus restricted to the use of a cheaply available gaseous medium, such as atmospheric air, whereas a gaseous medium of greater vsults. a

My object in the present invention is to devise a method and apparatus whereby a denser gaseous medium may be employed '.without material loss of the medium to the atmosphere. I attain my object by enclosing themout-h of the chamber in which the gaseous medium is allowed to expand with a thin flexible diaphragm of large area and by returning the gaseous medium to the chamber from which it was originally forced to and past the diaphragm.

The invention is hereinatter described and illustrated in the drawing, which is a vertical section of the apparatus constructed in accordance with my invention.

1- is a chamber, with which communicates a conduit 2 communicating with the smaller end of the horn-shaped chamber 3. The

larger end of the horn-shaped chamber com- 4 0 municates with, the annular chamber 4, with which communicates a conduit 5 communicating with the chamber 6 which, in turn, communicates through an opening 7 with the interior of the chamber 1. To the outer 4a rim of the annularcchamber is secured a thin, light diaphragm 15, pgeferably formed of paper, gold-beaters s other such material, it being important, however, that the dia hragm be substantial] air tight. A close circuitis thus provide through which a stream of a gaseous me-.

dium may be circulated. To efiect such a circulation I provide the blower 8, wh ch 1s shown-as of the Root type, and which is assing the diaphragm. After expansion t e gaseous density will give better re-- 11, celluloid, or

located within the chamber 6, the discharge vided in the upper part of the chamber 6 to also aid in suppressing pulsations due to the operation of the blower.

Betweenrtbe conduit 2 and the chamber" 3 I provide a constricted throat 11. Preferably this throat is adjustable in cross sectional area. A simple method of providing adjustabilit is to form the throat of a-sectionof rub er tubin and to apply thereto a clamp 12, the mova le member 13 of which is adapted tobe actuated by the screw 14.

'Baflles 16 positioned in staggered relationship form a zig-za'g passage through the chamber 1, and these diaphragms are preferably formed'of aporous material. Means are providedfor keeping thesebafiles constantly wetted. For-this purpose I show the upper edge of each battle as secured to the sprinkler tube 17 These are supported by branch .tubes 18, which. extend through the top of the chamber 1 and are connected with a liquid su ply pipe 19. -Separate valves 20 are provi edto control the flow through each branch pipe.

' A valve controlled pipe 21 provides means whereby the-chamber 1 may be filled with a suitable as. Preferably a pipe 22 leading from the'camber 1 communicates with the interiorof a gasometer 23 of ordinary type whereby constant; ressure may be main-f tained within the c amber 1. As the gaseous medium moves in aclosed circuit, and there 1s substantially no waste,.a relatively densegas such as carbon dioxide or sulphur dioxide may be employed. r' Save for the employment of. the closed circuit, the operation of the device substantially as in my co-pendlng 'apphcatlon hereinbefore referred to. T

The gaseous stream enters the conduit 2 A to the pump to be compressed. Atthe small end of the horn-shaped chamber 3 the diaphragm 24 is positioned. This may be arranged as usual to either receive or impart vibrations and is shown as of the electromagnetic type commonly employed in loud speakers.

It will be understood, of course, that the device is equally useful in transforming sound waves into mechanical movements of a diaphragm.

Many variations are, of course, possible of the means for circulating the gaseous medium which will fall within the scope of my invention.

What I claim is:

l. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in em ploying as the transferring medium. a

stream of a gaseous medium contacting with stream of compressed gaseous medium contacting with the diaphragm and moving in a closed circuit, causing the formation in said medium of liquid in a finely divided state prior to contact with said diaphragm, expanding said medium into contact with a second larger diaphragm, and returning the gas for recompression.

4. The method, of imparting vibrations from a vibratable diaphragm to the atmosphereor vice versa, which consists in em ploying as the transferring medium a stream of dense gaseous medium contacting with-the diaphragm and moving in a closed -'circui't, expanding said stream in'cross sectional area into contact ,with a second larger diaphragm, and returning the gas for re compression. 7

5. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a dense gaseous medium contacting with the diaphragm and moving in a closed circuit, causing the formation in said medium of liquid in a finely divided state prior to contact with said diaphragm, expanding said stream incross sectional area into contact with a second larger diaphragm, and returning the gas for recompression.

6. An acoustic transformer comprising a chamber increasing in cross sectional area from one end towards the other, a vibratable diaphragm at the smaller end of the chamber; a larger vibratable diaphragm closing the other end of the chamber; and

means for continuously introducing a gaseous medium into the smaller end of the chamber and for withdrawing it from the" larger end for re-use.

7. The method of imparting vibrations from a vibratable diaphragm to the atmosphere or vice versa, which consists in employing as the transferring medium a stream of compressed gaseous medium contacting with the diaphragm-and moving in a closed circuit, causing the formation in said medium of liquid in a finely divided. state prior to contact with said diaphragm,

expanding said medium in volume of cross sectional area. into contact with a second larger diaphragm, and returning the gas for recompression.

8. An acoustic transformer comprising a chamber increasing in cross sectional area from one end towards theother, a vibratable diaphragmat the smaller end of the chamber; a larger vibratable diaphragm closing the other end of the chamber; and means for continuously introducing a gaseous medium into the smaller end of the chamber:

and for withdrawing it from the larger end for re-use including a conduit having a constricted throat communicating with the smaller end of the chamber.

Signed at Highland Park, 111., this third day of March, 1927. PERCY A. ROBBINS. 

